Adam McQuaid was diagnosed with a strained left shoulder and could miss up to 3-4 weeks. The defenseman would return by the end of the regular season.

McQuaid was injured in the first period of Tuesday’s game when Eric Tangradi checked him into the end boards. McQuaid used his left arm to brace his fall, and skated only two shifts.

McQuaid, the Bruins’ No. 6 defenseman, has one goal and three assists in 25 games and is averaging 14:18 of ice time. McQuaid is also one of the team’s tough guys. He has five fights, including Saturday’s scrap with Washington’s Matt Hendricks.

Aaron Johnson will replace McQuaid in the short term. Johnson has been a healthy scratch for 22 games.

The Bruins are now without three players: McQuaid, David Krejci (right leg, day to day), and Chris Kelly (broken left tibia, return unknown).

The hobbled roster is one of the issues the Bruins hope to address partly via the trade market. Whether that market develops remains to be seen.

Heading into Wednesday’s games, Colorado was the only team in the Western Conference that was 6 or more points out of the final playoff spot. In the Eastern Conference, Buffalo, Washington, and Florida fit that description.

Unless more teams tumble down the standings prior to the April 3 trade deadline, Bruins general manager Peter Chiarelli may not be able to acquire the pieces — a left-shot top-four defenseman, a scoring wing, a depth blue liner — that could help stabilize his club’s shortcomings.

But the banged-up Senators, who ought to swap their team bus for an ambulance, are only 3 points behind the Bruins for second place in the Northeast Division. GM Bryan Murray will not part with unrestricted free agents-to-be when his club can qualify for the playoffs. The way Robin Lehner and Ben Bishop are stopping pucks, Ottawa will make opponents nervous in the postseason.

Two years ago, Chiarelli made early moves by acquiring Chris Kelly, Rich Peverley, and Tomas Kaberle. It appears Chiarelli will not be able to make similar preemptive strikes. Teams that will eventually become sellers may not make that determination until April 3.

So for now, the Bruins must look inward to snap their two-game losing streak. It is the first time in more than a year that they have dropped back-to-back games in regulation.

It could have been a different outcome had Patrice Bergeron (first period) and Zdeno Chara (third period) finished point-blank opportunities Tuesday night. Instead, Jets goalie Ondrej Pavelec used his glove to rob Bergeron and his lightning-fast right pad to boot out Chara’s bid.

“It’s frustrating when we get the amount of opportunities that we did tonight and they don’t go in,” Brad Marchand said after the loss. “Most of the time, you’ll get a few goals, three or four goals, in a game like that. You’ve got to give it to their goalie. He played pretty good. We hit a couple posts. That’s how it goes.”

Milan Lucic and Nathan Horton, centered by rookie Ryan Spooner, put only three shots on goal. The No. 3 line of Jay Pandolfo, Peverley, and Jordan Caron (two total shots) has shown little offensive presence.

It’s possible that once Krejci returns, Spooner could stick with the varsity to give the third line more offensive pop. Krejci would go back to his usual post between Lucic and Horton.

Spooner could slide to No. 3 center, Kelly’s former position, allowing Peverley to move back to right wing and Caron to move to the left side. Spooner (two shots, 15:29 of ice time) looked far more comfortable against Winnipeg than he did in Montreal during his NHL debut. Coach Claude Julien has deployed Pandolfo to assume some of Kelly’s penalty-killing responsibilities. Caron and Krejci have killed penalties before.

The Bruins also need to be more assertive on the power play. They entered Tuesday’s game averaging only 2.89 power-play opportunities. They drew four penalties against the Jets, but put only four pucks on goal during eight minutes of man-advantage time. Tyler Seguin, the half-wall quarterback on the No. 1 unit, tried to hit Spooner backdoor several times. Seguin should be more aggressive about skating the puck off the wall and shooting.

Had the Bruins stretched their lead, they could have withstood a rally. Instead, the Jets found a one-goal deficit simple enough to overcome.

Opponents once trembled at trailing the Bruins in the third period. Just this month, Montreal, Washington, Pittsburgh, and Winnipeg have proven that third-period deficits are no reason to say good night before the final buzzer.

“When we have third-period leads, we’re usually good at capitalizing and shutting teams down,” Johnny Boychuk said. “Lately, we’re letting them back in the game. We should be stepping on the pedal and going after them to score the next goal to push them down even further.”

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